If you don’t find anywhere in Northumberland, Silvercraigs at Kirkcudbright has no limit on how many well behaved dogs & doesn’t charge for them either. I’ve seen agility clubs with multiple dogs at Drumroamin Farm outside Newton Stewart, but that’s even further from the border.
If you find a site you like the look of, don't just rely on published info, phone and ask them.
A friend has very few refusals for her SIX dogs (Border collie x3, spaniel cross, poodle and a Yorkie cross), if necessary she sends photos of her 'dog garden' that keeps them confined to pitch, and a reference from a camp site she uses regularly, but usually they take her at her word.
Other friends also don't seem to have much trouble taking more than 3 dogs when they ask.
camping and caravan club allow 4 Beadnall Bay, havnt stopped there though have stopped at Seafields at Seahouses but its a 5 star site with prices to match. we have 3 and are stopping at Springhill Farm in Sept, not stopped there before, if it is out of season and you ask politely they may say yes
A day of all things motorhome and campervan. The show is held both in the main indoor arena and across the grounds. Catering, hot drinks and food options are available. Easy access to the site and free parking included. Win one of five pairs of day tickets